The present invention relates to an infrared (IR) imaging array which includes Schottky-barrier detectors, and more particularly to isolation means for the detectors for such an array which provides for a more compact array.
Schottky-barrier infrared (IR) charge coupled device (CCD) image sensors include a plurality of Schottky-barrier IR detectors arranged in a row for a line array or in rows and columns for an area array and coupled to a CCD which provides a read-out of the signals from the detectors. One type of Schottky-barrier IR detector includes a layer of either platinum silicide or palladium silicide on P-type conductivity single crystalline silicon with an N-type conductivity guard band surrounding the silicide layer. The guard ring serves to eliminate dark current spikes which could occur as a result of high field regions at the perimeter of the Schottky barrier. In order to isolate adjacent detectors from each other so as to prevent leakage and cross-talk between adjacent detectors, it has been the practice to provide P+ type conductivity channel stop between adjacent detectors.
The resolution of such an imaging device depends on the number of detectors in the array. The larger the number of detectors, the better the resolution. To achieve television-type resolution, it is necessary to have an array which is 512 detectors by 512 detectors. The larger the array, the larger the substrate that is required to make the device. In order to maintain the device as small as possible and thereby use a minimum size substrate, it is desirable to make the detector array as compact as possible. Another factor which has been a limitation in the development of the IR-CCD image sensors is the fill factor. The fill factor is defined as the ratio of the active detector area to the total pixel (picture element) area. Heretofore, the fill factor has been relatively low. One of the features of the detector array which affects its size is the isolation means between the detectors, i.e. the guard ring and channel stop. For example, the isolation means generally takes up about 20 micrometers of silicon real estate around each detector, which is about 42% of the length of each detector active area which is about 48 micrometers. Therefore, it would be desirable to reduce the size of the isolation means so as to reduce the overall size of the array while still maintaining the necessary isolation between the detectors of the array.